Alpha2-adrenoceptor agonist medetomidine affects the melatonin rhythm in rats.
We investigated whether alpha2-adrenergic mechanisms participate in the regulation of the daily melatonin rhythm. Female Wistar rats, living under 12:12 h light-dark conditions, received a subcutaneous injection of saline or medetomidine (alpha2-adrenoceptor agonist; 100 microg/kg) 1 h after lights off. Thereafter they were kept in continuous darkness. Pineal glands were collected for melatonin measurements at 2-h intervals during the first and second subjective nights. During both nights, a significant elevation of melatonin levels in medetomidine-injected rats was found 2 h later than in control rats. We interpret the first-night delay to be a sign of medetomidine's suppressive effect on melatonin synthesis, and the second-night delay a medetomidine-induced resetting of the circadian clock controlling the melatonin onset.
Laakso
M L
ML
Institute of Biomedicine, Department of Physiology, University of Helsinki, Finland.
Mustanoja
S M
SM
Hätönen
T
T
Alila-Johansson
A
A
D000316:Adrenergic alpha-Agonists / Q000494:pharmacology*; D000704:Analysis of Variance; D000818:Animals; D002940:Circadian Rhythm / Q000187:drug effects*; D005260:Female; D007093:Imidazoles / Q000494:pharmacology*; D020926:Medetomidine; D008550:Melatonin / Q000032:analysis*; D017440:Photoperiod; D010870:Pineal Gland / Q000737:chemistry*; D051381:Rats; D017208:Rats, Wistar; D013997:Time Factors
D000316:Adrenergic alpha-Agonists; D007093:Imidazoles; D008550:Melatonin; D020926:Medetomidine